STM32H533 trying to use the oscillator guidelines (AN2867)

[thansen]

I'm trying to calculate if I need an external resistor with my HSE crystal (24MHz, 18pF, 50R) but the suggested formula example does not give the shown result. So is the formula or the result wrong or have I misunderstood something?

Below example from AN2867:

 

An initial estimation of RExt is obtained by considering the voltage divider formed by RExt and CL2. Thus, the value of RExt is equal to the reactance of CL2.
Therefore, RExt = 1 / (2 π F CL2), and so, with an oscillation frequency of 8 MHz and
CL2 = 15 pF, we have RExt = 1326 Ω.

 

If I put the values mentioned in the formula I do not get 1326R??

 

 

 

[MHoll.2]

Why not? 

Rext = 1/( 2 * 3.1416 * 8e6 * 15e-12) = 1326

 

[thansen]

You are right but I did calculate it twice before my post and got the same wrong result each time??????

Sorry for the confusion!